A process for producing a semiconductor device includes various process steps such as a lithography step, an etching step, and an ion injection step. After the termination of each of the steps and before shifting to the next step, a cleaning step and a drying step for purging a surface of a wafer by removing impurities and residues remaining on the wafer surface are performed.
For example, in the wafer cleaning step after the etching step, a chemical liquid for a cleaning treatment is supplied to the wafer surface, and then pure water is supplied to perform a rinsing treatment. After the rinsing treatment, a drying treatment for drying the wafer by removing the pure water remaining on the wafer surface is performed.
As a method for performing the drying treatment, for example, a method of drying the wafer by substituting the pure water on the wafer with isopropyl alcohol (IPA) has been known. However, there has been a problem that a pattern formed on the wafer is collapsed by surface tension of the liquid, at the time of the drying treatment.
In order to solve the problem, supercritical drying by which the surface tension is nullified has been proposed. For example, IPA on the wafer is dissolved into the supercritical CO2 fluid by bringing a wafer of which a surface is wet with IPA into a state of being impregnated into carbon dioxide (supercritical CO2 fluid) which is in a supercritical state in a chamber. Subsequently, the supercritical CO2 fluid into which the IPA is dissolved is gradually discharged from the chamber. After that, the wafer is dried by causing a phase shift from the supercritical CO2 fluid to a gas (vapor) by reducing a pressure and a temperature inside the chamber and then discharging the gas to the outside of the chamber.
However, in the phase shift of carbon dioxide from the supercritical state to the gas (vapor) by reducing the pressure inside the chamber, there has been a problem of deposition of particles caused by a drying mark or the like which is generated by cohesion and re-absorption on the wafer of IPA remaining in the chamber in the state of being dissolved into the supercritical CO2 fluid.